SYNTAX

The syntax of the lambda calculus is incredibly simple, because there are only three types of expressions:

	TYPE		syntax
	
	variable	string (e.g. "x", "y")
	
	application	(E E')  (where E and E' are both
				 lambda expressions)

	abstraction     \x.E    (where x is a variable
				 and E a lambda expression)

or using BNF:


	LAMBEXPR :: = VARIABLE 
                       | (LAMBEXPR LAMBEXPR)
		       | ("\" VARIABLE "." LAMBEXPR)

Note that the two pieces of concrete syntax (the period and lambda
symbols) have been explicitly quoted.

Which of the following are legal lambda expressions:

1. x

Yes No

2. \x.

Yes No

3. \x.yx

Yes No

4. \x.\y.xyxx

Yes No

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